1. Field of the Invention
The present invention relates to a method of making a three-dimensional sintered product in which a target object is obtained by sintering and hardening powder material layers with an optical beam, especially relates to a method of preparing a metal mold by uniting a plurality of lamination made of metallic powder layers sintered by a laser beam.
2. Description of the Related Art
Japanese Patent No. 2620353 discloses a method of making a three-dimensional object known as photo-shaping. According to this Patent, an optical beam L is first irradiated on a predetermined portion of a layer of powder material, which is either an organic material or an inorganic material, to form a sintered layer. The sintered layer thus obtained is then covered with a new layer of powder material, and the optical beam L is irradiated on a predetermined portion of the new layer to form a new sintered layer, which is united with the underlying layer. These steps are repeatedly carried out to form a sintered product or three-dimensional object in which a plurality of sintered layers are firmly laminated one above another. According to this method, the irradiation of the optical beam L is conducted based on sectional form data of each of the layers that are obtained by slicing a model of design data (CAD data) of the three-dimensional object into a desired thickness. For this reason, without a CAM device, the method referred to above can be used to make a three-dimensional object of an arbitrary shape and to obtain any shaped object of a desired shape quickly, compared with a conventional cutting and machining method.
According to this method, however, considering problems such as warping and cracking due to moulding times and internal stress, this method should be carried out by sintering necessary portions into a higher density and remaining portions into a lower density rather than by sintering all the portions into a same density. For example in case of metal mold for injection moulding, surface portions for transcription of object and piping portions for cooling water should be formed in a higher density and remaining portions should be formed in a lower density.
The higher density sintered layers have a very smooth finished surface due to almost complete melting and solidification, thereby keeping water proof of cooling water piping. However, the layer of powder material having a density of 50 to 60% will be sintered to the higher density layer having a density of almost 100%, so that as shown in FIG. 16, when the powder material layer 10 having a thickness of t0 will be sintered into the higher density layer 11H by an optical irradiation, the surface level of the higher density layer will be lowered by a difference [δ] from the original surface level of the powder material layer.
Further, when the thickness of the powder material layer is determined by a sinking amount of the stage 20, a thickness of the powder material layer is set to a value larger than a predetermined value [t] and furthermore, when the powder material layer 10 will be sintered by a sintering condition of higher density, the resulting surface of the higher density layer will be lowered by a stage difference [δa] (difference [δa] is larger than difference [δ]).
Further, another powder material layer 10 is formed on the higher density layer 11 and sintered under a condition for the lower density to form a lower density layer 11L. As shown in FIG. 18, the powder material layer 10 becomes thicker by the above difference [δa] in this case.
In this method, since the optical beam condition for lower density is determined according to a predetermined thickness [t] of the powder material layer 10, the optical beam having a predetermined condition can not make the powder material thicker by difference [δa] than a predetermined value [t] sintered completely, thereby not giving an enough adhesive power to the resulting lower density layer which is easy to be peeled from the higher density layer.